说明：  哈夫曼编码：输入一个文本文件（英文文本），剔除其中的非英文字符，并将英文字符统一转化为大写字符，然后统计各个字符的出现概率。创建哈夫曼树，给出编码表（即各字符的码字）及编码效率（带权路径长度）
(Huffman Coding: Enter a text file (English version), excluding one non-English characters and English characters converted to uppercase characters reunification, and then the emergence of statistical probability of the various characters. Create a Huffman tree, given encoding table (that is, the character code word) and the coding efficiency (with the right path length))